Kinetic and Thermodynamic Investigations of Fuchsin Basic Dye Adsorption onto Graphene Oxide/Polyvinylpyrrolidone/Acrylic Acid Nanocomposite Hydrogel: Equilibrium Modeling, pH Influence, and Ionic Strength Effects

Abstract

Free-radical polymerization was used to create a nanocomposite hydrogel of graphene oxide, polyvinylpyrrolidone, and acrylic acid (GO/P(PVP-AAc)) to adsorb Fuchsin Basic (FB) dye from aqueous solutions. FTIR, XRD, and FESEM validated the nanocomposite's structural and morphological properties. Batch adsorption experiments assessed the impact of various parameters, such as contact time, initial dye concentration, solution pH (1-10), ionic strength (NaCl, KCl, and CaCO₃ electrolytes), adsorbent dosage, and temperature (288-308K). The kinetic behaviour of the adsorption process was analyzed by applying both pseudo-first-order and pseudo-second-order models, and the results demonstrated that the process conformed more closely to the pseudo-second-order model, with a correlation coefficient (R²) of 0.9985. Equilibrium data were fitted to different isotherm models, among which the Freundlich model provided the best fit, thereby suggesting a heterogeneous multilayer adsorption mechanism. Thermodynamic evaluation through the calculation of ΔG°, ΔH°, and ΔS° indicated that the adsorption was both spontaneous and exothermic in nature. Under optimum conditions—neutral pH and a temperature of 288K, the maximum adsorption capacity reached 172.41mg/g. Furthermore, the swelling behaviour, recyclability, and reusability of the hydrogel were assessed and found satisfactory. Overall, the findings of this study point to the GO/P(PVP-AAc) nanocomposite hydrogel as a viable and cost-effective candidate for the treatment of FB-contaminated wastewater.